Modern Epoxy resins have become commonplace in the shops of both amateur and professional wooden boat restorers. Properly used, epoxies can save a considerable amount of time and money in the restoration or repair of a boat. Improperly used, however, they can be a hazard both to the user and to the boat they are being used on.
Types of Epoxies
There are several different types of epoxy available today, Mainly Resins (liquid) and Putties. Epoxies are multiple part, meaning that in order to use them you must mix two or more components together. When the parts are mixed, a chemical reaction occurs, which results in the hardening of the epoxy. Different types are suitable for different jobs-
Resins
Liquid resins are the most versatile of the types. Consistencies vary from watery to more like honey, depending on the brand and intended usage. Liquids can be used as they are, or mixed with a variety of fillers to achieve different working, curing, or strength characteristics. Used plain, they can be used as glue, to 'wet out' fiberglass cloth, seal plywood, and more. Mixed with appropriate fillers, they can become various types of fillers, formulated for strength, sand ability, or a combination of the two. Liquid resins are mixed with different hardeners to achieve different curing results, as an example to give a longer working life before the resin cures or to achieve a super clear end result for varnishing. Resins are mixed with hardeners by ratio, some of the more common being 3-1 and 5-1. Examples of this type of epoxy include the brand names West Systems, System 3, and Epiglass. All of the following techniques were developed with resins in mind.
Putties
Epoxy putties have quite a few good uses in restoration as well. Most putties on the market today are formulated mainly with strength and/or a fast cure time in mind. Different brands come in different consistencies, that range from peanut butter to play dough. The thicker formulas are often workable by hand, which is ideal for quick repairs. Most putties can be used anyplace you would use thickened resins.
Essential Tools
You need to have a few basic tools on hand when you are going to work with resins. Epoxy hardeners are strong sensitizers, so you should protect your skin from contact with both the resin and the hardeners. Use a pair of disposable latex or vinyl gloves. You will want to have several mixing pots, the best ones are flexible plastic. A few sturdy mixing sticks, disposable brushes, and a roll of masking tape will also come in handy. Uncured epoxy can be cleaned up with a solvent made specifically for the purpose (most epoxy manufacturers have their own) or lacquer thinner. You also need a means of accurately measuring the epoxy and hardener, if you are on a tight budget any graduated cups will do, but it is much easier to buy the dispenser pumps made by the resin manufacturers specifically for that purpose.
Mixing Epoxy
Before you can use epoxy resin, you have to mix it in the appropriate ratio. The ratios used vary from manufacturer to manufacturer, so consult the information that came with the epoxy. Some product comes with pumps that deliver the appropriate quantities for convenience. Operate the pumps slowly making sure to depress fully until you reach the stops. Pumps that have not been used for a time may collect air and delver incorrect quantities. You can mix a test batch of one pump stoke each to be certain the pupms are delivering the proper quanties. It's a waistful procedure, however, it's no fun to remove uncured epoxy from your project.
1. Measure out the proper amount of resin into a container, leaving room for the hardener. Measure the hardener in a separate container.
2. Then add it to the resin. Mix the epoxy thoroughly, but slowly making sure to reach all the surfaces of the container.
3. Mixing too fast will allow bubbles to get trapped in the epoxy, which will get in your way later.
Fillers
The type of filler that you use will depend on what you want the epoxy to do. There are fillers available for making adhesives, for high strength structural filling, and easy sanding fairing fillers. Consult the technical information for the epoxy manufacturer to determine which is correct for your use. Add the filler after the epoxy resin has already been thoroughly mixed.
1. Pour the filler into the epoxy, and stir it thoroughly.
2. Add more or less filler to achieve the desired thickness, but do not exceed the manufacturers recommended maximums.
Filling a small hole, gap, crack, or void
Areas that have small holes, gaps, cracks or voids to be filled should be dealt with as follows:
1. Isolate the repair area. Find the extent of the damage.
2. Gouge any damaged or rotten wood out of the repair area, using a chisel, wire wheel, etc. This will both remove any weak material and also make room for the epoxy and filler mixture.Be sure, especially when you are dealing with rotten wood, that you go all of way down to sound new wood, or your repair will be weak. Mix the epoxy and appropriate filler, following steps above. You will generally use a high strength filler for this type of work.
3. Apply the resin/filler mixture to the repair, and work it in place with a putty knife or resin spreader. Allow ample cure time, then sand any tool marks or imperfections. The repair is now complete!
Repairing bigger areas
Bigger repair areas can't be filled with epoxy and filler alone, both for reasons of the high cost of the epoxy and also the weight. In a case like this, it is best to do the following:
1. Isolate the repair area.
2. Cut the ends of the area at an angle. this provides ample area for the epoxy to adhere to. Make sure you go beyond the damaged wood. When both sides of the area to be repaired have been properly cut, measure the size of the hole and cut a "dutchman", or a block of wood that fits into the hole loosely. You do not wat a perfect fit, or else there will not be room for the epoxy.
3. Put the dutchman in place, using a generous amount of epoxy at both ends.
Repairing rot damage near a bolt hole
Water leaking in alongside a bolt hole (as in a stem) will often lead to rot damage along all or part of the bolt hole.
1. Block showing bolt hole in need of repair.
2. To repair it, you need to remove the rotten wood with a chisel or drill.
3. Fill the hole completely with epoxy and a high strength filler mixture, allow it ample time to cure.
4. Then re-drill the hole for the bolt.
Laminating with epoxy
You will often need to laminate two or more pieces of wood together in order to get a piece of wood of a desired thickness. Epoxy makes an ideal adhesive for this purpose. Make sure that the parts to be joined are clean and dry. Brush an ample amount of either un-thickened epoxy or epoxy with a small amount of adhesive filler in it on both parts to be joined. Clamp the parts together securely, and keep them clamped until the epoxy has cured. Properly done, this is as strong as a single piece of wood.
A note on Epoxy Safety by Sam Devlin of Devlin Designing Boat builders:
Sam Devlin on Safety
The most controversial aspect of epoxy use is the matter of safety. There is no way around it: the improper use of epoxy can be injurious and hazardous to your health. But constant vigilance and continuous care for safe and proper use will minimize the hazard. Boatbuilders using normal precautions and staying safety-minded at all times can use epoxy with the best of results while fully protecting their health. Wear safety glasses, respirators and gloves. Tyvek suits are great protection.
The strongest advice I can give you is to keep epoxy off your skin. Prolonged contact with the resin and hardener can cause an allergic reaction--sensitization--in some people. Once sensitized, the slightest contact with the resin and hardener, their fumes, or even standing dust from epoxy that hasn't fully cured can bring on a reaction.
Keep epoxy off your tools, and always wear gloves that protect wrists as well as hands. I know of three examples where boatbuilders threw caution to the wind and suffered the consequences. Two were first-time builders of boats, but one was a professional who should have known better. The common denominator was failure to use proper gloves. The professional was a reckless fool in all aspects of his life. He refused to use gloves and would plunge his hands into acetone at the end of each job to clean off half-cured resin. While using urethane paints, he would refuse to wear even the simplest dust-filter mask, let alone an organic-vapor respirator or even a fresh-air system. Predictably, he experienced lung damage from the urethane paint and spent several days spitting up blood. In addition, the exposure to the epoxy caused a rash on both wrists and his forehead that resembled a reaction to poison oak. The rash would disappear after five or six days if he stayed clear of epoxy, but as soon as he walked back into the shop, it would reappear. In the end, he had to give up boatbuilding with epoxy altogether, and the last I heard of him, he was at work in a can factory.
Most gloves available to boat builders are adequate for epoxy but will never stand up to cleanup solvents such as acetone or lacquer thinner. When cleaning up, discard the thin latex gloves you used for epoxying and don heavy, solvent-proof gloves.
And then there's "Devlin's Law", a variant of Murphy's Law. After a goodly amount of experience I have identified three natural temptations that you will experience when you are working with epoxy. Once you have epoxy on your gloves, you WILL have an itch on your nose, your eyes WILL need to be rubbed, and you WILL begin to sweat and need to wipe your brow. I guarantee you'll experience these urges, and just as surely, if you succumb to temptations, you will experience some nose or eye sensitization due to epoxy exposure.
There is simply no alternative to constant vigilance: using safety gear, working as cleanly as possible, and not getting epoxy on your skin. Keeping Devlin's Law in mind, one reason for wearing a canister respirator--apart from the fumes and dust--is to keep yourself from scratching your nose.
After fifteen years of using epoxies almost daily, the only reaction I notice is a slight constriction of the throat during extended use. But when I use a respirator, I never experience the throat irritation.
Of the two epoxy components, the hardener is the most toxic. Keep this in mind, particularly when cleaning the hardener side of your epoxy dispenser. Extreme caution should also be used when sanding partially cured (green) epoxy surfaces, as may happen in the winter in an unheated shop. Always wear a respirator and protective clothing, even if it's only street clothes that are laundered daily and cover all parts of the body likely to come in contact with uncured epoxy. If you insist on keeping your beard, a full-hood, powered-respirator fresh-air system may be the only answer, since regular cartridge-type respirators will not seal properly over a beard.
The bottom line, my macho friends, is to respect these chemicals; just because the hazards are invisible does not mean they are absent.
I have seen a couple instances of almost magical acts of reverse gravity in which epoxy or its resin and hardener components splashed up into boatbuilders eyes. In each instance we had to rush the victim outside to a water hose for a lengthy flushing of his eyes. Then rush him to the emergency room where the doctor repeated the process--not something anyone would do by choice. Wear eye protection at all times. Safety glasses don't work well for me because I find them uncomfortable. And if eyeglasses are uncomfortable, at some point you'll find yourself working without them--and that's when accidents happen. Even if you don't wear eyeglasses for vision, get yourself fitted with a proper expensive set of frames with clear lenses. Spend some money on them so you won't treat them casually and wreck them. Then wear them constantly in the shop so you get used to them.
And even the protection can't be taken for granted. I've also seen a worker develop nasty looking, painful hands as a reaction to latex disposable gloves, which in his case was probably a reaction to the talcum powder in them. He was fine after he switched to non-talc gloves over soft lightweight cotton liner gloves.
Moderation is the best protection. Always shower after a work session; it will help keep your body clean and healthy. Also don't forget to launder your clothing often. Wearing the epoxy-encrusted clothes day after day just continues to expose you to uncured resin or hardener.
One of my fellow members of the Indiana Chapter of ACBS has an Antique Boat Shop curiously called "The Antique Boat Shop" in Fort Wayne Indiana. They work somewhat exclusively on classic runabouts. Chris-Craft, Century, Gar Wood, etc. The do some very nice work and have a straight forward philosophy. 
